Syrian chemical weapons being removed from the country on a Danish cargo ship in 2014.
Photograph: Petros Karadjias/AP

Evidence that the sarin nerve agent was used in the chemical attack that killed more than 80 and injured hundreds of others in Syria’s northern province of Idlib last week has triggered awkward questions for the government over the part played by the UK in the Assad regime’s development of a chemical weapons programme.

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Human rights groups and arms control campaigners have highlighted the government’s own admission that in the 80s the UK exported the chemicals necessary to make sarin to the Syrian regime. The UK also sold specialist equipment after the millennium which it now appears was diverted to the chemical weapons programme.

Allegations that the UK supplied potentially deadly chemicals to Syria were investigated by the Committees on Arms Export Controls (CAEC) which in 2013 wrote to then business secretary, Vince Cable, asking him to disclose the names of companies given licence approval between 2004 and 2012 to export to Syria chemicals that could be used to manufacture chemical weapons. Cable was criticised by the committees for refusing to disclose the names of the companies.

Sir John Stanley, chairman of the CAEC, said: “The effect of the business secretary’s refusal to date to disclose the names of the companies is to prevent the committees from taking evidence from them. This is a serious matter both for the four select committees who constitute the CAEC and for the House of Commons as a whole. I have therefore written to the business secretary asking him to reconsider his decision.”

Export data collected by Campaign Against the Arms Trade, which dates back to 2008, provides no evidence that any chemicals were supplied to Syria in the last nine years.

The lifespan of a weapon is often longer than the lifespan of a government that they are sold to

Hague revealed that the exports included several hundred tonnes of the chemical dimethyl phosphite (DMP) in 1983 and a further export of several hundred tonnes in 1985; several hundred tonnes of trimethyl phosphite (TMP) in 1986; and a quantity of hydrogen fluoride (HF) in 1986 through a third country.

Hague told parliament: “All these chemicals have legitimate uses, for example in the manufacture of plastics and pharmaceuticals. However, they can also be used in the production of sarin. DMP and TMP can also be used for the production of the nerve agent VX. That is why the export of such goods is strictly prohibited under the UK export regime introduced since the 1980s and progressively strengthened.”

He added: “From the information we hold, we judge it likely that these chemical exports by UK companies were subsequently used by Syria in their programmes to produce nerve agents, including sarin.” A review also confirmed the export of ventilation fans by a UK company to Syria in 2003. The Syrian regime appears to have diverted the fans for use in a chemical weapons facility, Hague admitted.

“The lifespan of a weapon is often longer than the lifespan of a government or the political situation that they are sold in to,” said Andrew Smith of Campaign Against Arms Trade. “When arms or chemical components are sold there is no way of knowing when they will be used or who they could be used against. By the UK government’s own admission it has sold components to Syria that can be used in the production of chemical weapons. It must now conduct a full investigation to determine if they were used in these terrible attacks and publish a list of other regimes and governments they have been sold to.”

A chemical weapons expert who advises Amnesty International and asked not to be identified, suggested it would be hard to preserve any sarin manufactured decades ago: “It is difficult to safely make pure, high-quality sarin that will not decompose and degrade rapidly after production. It requires a good deal of specialised equipment and expertise, as well as some special state-of-the-art information that is not generally found on the web or in libraries.”

Allan Hogarth, head of policy and government affairs for Amnesty International UK, said the Assad regime’s alleged use of chemical weapons was a timely reminder to the UK that it needed to be vigiliant about what it exported and to whom: “Even if it proves impossible to establish the origins of the chemicals used in the appalling Khan Sheikhun attack, it’s vital that we maintain absolutely watertight controls over what chemicals we export and to who.

“In the past the UK has been far too lax over these matters, something that improved with the implementation of EU-wide and other international measures. The UK should be ensuring that these standards aren’t compromised when pursuing Brexit trade deals and that all the relevant controls are maintained or tightened still further.”